A large conductance, Ca2+-activated K+ channel in a human lung epithelial cell line (A549)

AbstractA large conductance, Ca2+-activated K+ channel in a human lung epithelial cell line (A549) was identified using the single channel patch clamp technique. Channel conductance was 242±33 pS (n=67) in symmetrical KCl (140 mM). The channel was activated by membrane depolarization and increased cytosolic Ca2+. High selectivity was observed for K+ over Rb+(0.49)>Cs+(0.14)>Na+(0.09). Open probability was significantly decreased by Ba2+ (5 mM) and quinidine (5 mM) to either surface, but TEA (5 mM) was only effective when added to the external surface. All effects were reversible. Increasing cytosolic Ca2+ concentration from 10−7 to 10−6 M caused an increase in open probability from near zero to fully activated. ATP decreased open probability at ∼2 mM, but the effect was variable. The channel was almost always observed together with a smaller conductance channel, although they could both be seen individually. We conclude that A549 cells contain large conductance Ca2+-activated K+ channels which could explain a major fraction of the K+ conductance in human alveolar epithelial membranes